Optimal posture best for the body

SCAPULA: Aka, the shoulder-blade.

O, good sir, softly, good sir! I fear, sir, my shoulder-blade is out. (A Winter's Tale)
Posture is a topic for the physiotherapist to ponder at every moment, because unless they happen to be blind and are oblivious to witnessing the passing mob of humans across their visual field, every person we spot can and could, should be evaluated. Once you are trained in the scrutiny of the human posture, you simply cannot ignore it. Not that we are going to intervene if you are slouching to within an inch of your life, but posture is definitely advantageous to the layperson to seek training in because it will save you in a variety of mechanical ways.
The human body is a collection of joints connected in such a way that an ideal alignment of it will enhance the systems that go on inside. Some may argue that ideal posture is subjective, an opinion of a group of boffins, or an attempt to stifle free will or creativity. My argument is that there is a state, free of consequences in physics and biochemistry for the human frame. To call it normal is inaccurate because no one is normal, but perhaps optimal is the better word. Certainly anyone is welcome to train their body to stand or sit in whichever way they choose. It's just that optimal alignment has the least negative consequences. The good news, which I dispense an awful lot, is that optimal alignment is attainable and becomes easier with practice. I might add that I am speaking in general here, as there are some of you out there with an anomalous twist in your spinal column, or a sticky outie bum, or a dowagers hump. There are natural inherited variations that are not so possible to manage. This article will focus on the bulk of you without postural nuances outside of the box, so to speak.
Optimal posture will make breathing efficient and comfortable. It will enhance the removal of solid waste from your body. Digestion works best when you're upright so it stands to reason that every system within the body will work well in this direction. Notice what happens when people stay horizontal for too long. Sleeping in results in low back pain and headache. Of course the mechanics of the skeletal system are attuned to neutral posture. This is where all the forces are balanced. If you think of the spine as a tent pole holding up a marquee, when the best postural position is found, all the ropes are equally tensioned. You wouldn't want the tent pole to be unevenly loaded. So to come back from that analogy, too much imbalance over too long causes attrition to the spinal tissues. The popular slouch posture delivers many kilos of negative load to the discs. Upright sitting does much less.
Exaggerated good posture where the pelvis tips forwards giving you a bigger lumbar curve compresses the delicate arch structure of the vertebrae and forces the joint surfaces together. Good upright postural sitting does not. Not that I am advocating sitting. Apparently sitting is the new smoking, although they may relegate it to the new glue sniffing as sugar wants to be considered most dangerous and foolhardy.
Your shoulder blade is a fantastic example of the benefits investing in good posture. Firstly it sits on a rounded barrel and it can move in any direction. It is at one corner attached to the collar bone and the rest of it floats smoothly over muscle and bone anchored in a masterful array by 17 muscles. It is the foundation for shoulder movement. Most people will accept that the shoulder can be injured by traumatic incidents, but it is also commonly traumatised when the scapula is sitting outside of its optimal place. As you may have noticed, muscles can become tight, and so if the neck muscles (upper trapezius) become tight shrugging constantly sitting at a desk, the ball and socket will no longer move in their optimal way. Any of the muscles surrounding can weaken or tighten from habitual postures, and so the function begins to suffer. Long-term slouching rounds the upper back, and so to see ahead, we must pull the head backwards instead of intuitively correcting the slouch. The scapula doesn't work as well on a ball shaped chest, and so subtle micro trauma begins and over time develops into macro trauma. Add to that something equivalent to trailer tie downs - bra straps - cutting deep into your muscles, you will inevitably have lousy shoulders.
The term 'Dowagers Hump' is no longer stigmatising enough to discourage this upper thorax sag. In fact through Downton Abbey we have learned to love the dowager afresh thanks to Dame Maggie Smith's tour de force portrayal. Buffalo hump might make a comeback, however it is currently in use via Cushing Syndrome. Thoracic Kyphosis is available but too much jargon for the lay person.
I propose the Back Verandah Syndrome. It can be rated in severity by how many beverage vessels you can sit on it on a hot summer afternoon.
What can you do to prevent it, or to improve it? Steve August, a brilliant mad scientist in our physio ranks, invented the Backpod, a hard half rugby ball shape that sits between your shoulder blades as you lie on the floor. Pillows are stacked high in the beginning to make the entry into this hopeful habit bearable. Think of my knee placed between your shoulder blades and then me pulling on your shoulders towards me. Lying on the backpod, or similar rolled up towel, tennis balls or if you're American, Lacrosse balls, allows gravity to apply the reverse to what you have been doing all day. Sitting, slouching, mooching or hunching over a good crossword in a local cafe.
Another option is to have a physiotherapist scrutinise the habits of your scapulae as they hang out. Spotting deficits in timing and motion and positioning will give them the ammunition to dish out exercises, both stretch and strength based, to bring you back closer to optimal, and rectify the relentless plunge into inevitability in this sag happy, slouch comfy world.
Posture is optional but at the same time everyone has it. Rather than wait for an injury to occur, perhaps you could learn how to prevent dysfunction. If you are wondering what might become of your Lost in Space scapulae, or how to bring them home from the Delta Quadrant, get them seen to.